Hat Size Calculator
Convert head circumference to US hat size, letter sizing, and metric equivalents. Perfect for ordering fitted caps, fedoras, helmets, or sewing patterns.
US Hat Size
7 1/8
Exact: 7.16
Head Circumference
22.50" / 57.1 cm
Letter size: M
Fit Advice
Great! Your measurement aligns closely with standard hat sizes.
How to Use This Calculator
Measure your head
Use a soft tape measure around the widest part of your head—typically above eyebrows and ears.
Enter the circumference
Input in inches by default or switch to centimeters if that’s how you measured.
Review your size
Note the US size, letter equivalent, and fit recommendations before buying or sewing hats.
Formula
US Hat Size = Head Circumference (in) ÷ π
Centimeters = Inches × 2.54
Round the result to the nearest ⅛ to match typical hat size increments.
Example: Circumference 22.5" → 22.5 ÷ π ≈ 7.16 → rounded to 7 1/8.
About the Hat Size Calculator
Hat sizes can be confusing because some brands use numbers, others use letters, and helmets often convert to metric. This calculator gives you each reference so you can shop or craft without guesswork.
When to Use This Calculator
- Buying fitted hats: Snapbacks and flex-fit caps still need the right base size.
- Ordering helmets: Many sizing charts are based on head circumference.
- Sewing hat patterns: Convert measurement to the pattern’s size callout.
- Creating custom gifts: Ensure a perfect fit for handmade beanies or caps.
Why Use Our Calculator?
- ✅ Multi-unit support: Works with both inches and centimeters.
- ✅ Clear rounding: Shows exact size and the industry-friendly rounded value.
- ✅ Fit guidance: Understand whether to size up or down.
- ✅ On-the-go: Accessible from your phone when shopping.
Common Applications
Milliners: Quickly convert client measurements into block sizes.
Sports teams: Size team hats before placing a bulk order.
Outdoor enthusiasts: Ensure helmets and beanies fit for safety and comfort.
Tips for Best Results
- Measure twice for accuracy, especially if ordering online.
- Measure where you intend the hat to sit—higher or lower changes the size.
- If you’re between sizes, choose the larger size and use sizing tape inside the band.
- Different materials (felt vs. straw vs. knit) can stretch or shrink—adjust accordingly.
Frequently Asked Questions
Should I measure tighter or looser?
Measure snug but not tight—the tape should be comfortable. Hats often include sweatbands that add slight compression.
Can I convert to UK or EU letter sizes?
Most international charts rely on centimeters; use the provided centimeter value to match brand-specific charts.
What if my head is between sizes?
Adjustable hats accommodate variance. For structured hats, size up and add foam/sizing tape to the sweatband.
Do children’s hats use the same formula?
Yes—measure the crown circumference and convert the same way. Children simply fall into the smaller numeric sizes.